A wide variety of types of structures for disposable absorbent articles used to collect body fluids are known in the art. Commercially available absorbent articles include diapers, adult incontinence products, catamenials and bandages. Disposable products of this type comprise components for receiving, absorbing and retaining fluids. Typically, such articles include a liquid permeable topsheet, an absorbent core, and a liquid impermeable backsheet.
Disposable absorbent articles have previously been provided with elastic members to improve the side leakage performance of such products. For example, U.S. Pat. No. 3,860,003, issued to Buell on Jan. 14, 1975, discloses elasticized disposable absorbent articles wherein an elastic member is positioned in the side flap of the product between the topsheet and the backsheet. The side flap is gathered by the elastic member such that a boat-like configuration for the pad is presented and the side flaps form a barrier along the edges of the product.
An alternative way of providing an absorbent article with an elasticized side flap is to wrap a web of elasticated material, such as an elastomeric film laminate on the longitudinal side edges of the article. The elastomeric film laminate preferably comprises a soft outer coverstock layer so that the portion of the side flap that comes in contact with the wearer during use will be comfortable. A sanitary napkin having an elasticized side flap provided in this manner is described in U.S. Pat. No. 5,234,422. (See also the disclosure of European Patent Application Publication No. 0 534 488 A1, published in the name of Menard, et al., on Mar. 31, 1993.)
Various methods for attaching a web of an elasticized material such as an elastomeric film laminate to the side edges of an absorbent article for this purpose can be attempted. One suitable way for attaching the elastomeric film laminate along the longitudinal side edges of the article is by the use of adhesives. The adhesives can be applied in a variety of forms, including lines, beads, sprays, and spirals. Spirals are preferred because they can be applied in a relatively well defined strip of adhesive, and because the distance between the spirals can be spread out along the length of the strip so that less adhesive is used than if the adhesive were simply sprayed along the entire length of the strip.
One approach for applying adhesive in a spiral pattern to attach such a component or web to an absorbent article would be to apply the adhesive once to one side of the web and then to fold the web around the longituidinal side edge of the absorbent article attaching half of the web to the side of the absorbent article that will face the wearer's garment during wear and the other half to the side that will face the wearer's body during wear. Alternatively, the adhesive can be applied to the edges of the absorbent article on both faces of the absorbent article and the web can then be wrapped around and secured to the edges of the absorbent article.
Several problems arise in attempting to attach a web of material to the side edge of an absorbent article in such a manner, particularly when an adhesive application is used to attach the web. First, the adhesive has to be applied very close to the edges of the web of material so that the edges of the web of material will be bonded to the absorbent article. The formation of unbonded edges of the web of material may result in the web of material having a tendency to fold back and give the article an unsightly appearance. The need to apply adhesive close to the edges of the web of material, however, must be balanced against the problems caused when adhesive extends beyond the edges of the web of material. If the adhesive is sprayed beyond the edges of the web of material, the adhesive may be sprayed on the equipment used for assembling the sanitary napkin. In addition, spraying the adhesive beyond the edges of the web of material may cause the undesirable result of the adhesive being sprayed on a portion of the sanitary napkin that comes into contact with the consumer's skin, possibly causing these portions of the absorbent article to stick to the wearer's skin.
Other problems that arise are caused by a tradeoff that exists between the ability to apply adhesive close to both edges of the web of material and the strength of the adhesive bond that can be formed using the adhesive. For example, if it is necessary to create a stronger bond with the web of material, conventional processes which use a single application of adhesive to the web require sacrifices in the ability to apply adhesive near both edges of the web of material. For instance, when adhesive is applied in a spiral pattern, the amount of air pressure employed by the adhesive applying mechanism can be adjusted upwardly or downwardly while the adhesive flow rate remains the same. A reduction in the air pressure provides a smaller spiral pattern having more precisely defined edges. The smaller, more concentrated pattern of adhesive forms a stronger bond between the web of material and the absorbent article where the adhesive has been applied. However, when a single application of adhesive is used to coat the web of material, the smaller pattern results in a decrease in the ability to simultaneously apply adhesive close to both edges of the web of material. An increase in the amount of air pressure, on the other hand, results in a wider application of adhesive being applied to the web of material, which can more nearly approach both edges of the web of material. The increase in the amount of air pressure, however, results in a loss in control over the location of the edge of the application of adhesive. The increase in air pressure also results in a less concentrated adhesive application and, thus, a weaker bond with the web of material.
In addition, attaching the web of material to the edge of the absorbent article using a single application of adhesive provides no mechanism for control over the amount of adhesive applied when there are material variations which require different amounts of adhesive in order to form a secure bond with the web of material. For instance, there may be variations (such as normal manufacturing variations) in any of the materials associated with attaching the web to the absorbent article. The material variations can, for example, occur in the topsheet material, the web of material, and the adhesive used to attach the two. Any of these material variations may require a greater amount of adhesive to be applied to the web of material to form a secure bond with the web of material. There is no way to compensate for this using a single application of adhesive since, as noted above, concentrating the adhesive results in a reduction in the ability to apply adhesive near both edges of the web of material.
Thus, a need exists for improvements in the ability to control the application of adhesive materials to the webs that are to be attached to the side edges of an absorbent article. A need also exists for improvements in the usual methods for applying adhesives that will eliminate the tradeoff that exists between the ability to simultaneously apply adhesive close to both edges of the web of material and the strength of the adhesive bond that can be formed by the adhesive application. Further, a need exists for a method that provides control over the amount of adhesive that can be applied to secure a web of material to an absorbent article when there are variations in the materials used in the process.
It is, therefore, an object of the present invention to provide an improved process for attaching a web of material to the side edges of an absorbent article. In particular, it is an object of the present invention to provide improved control of the pattern of application of adhesive used to attach such a web to an absorbent article.
It is another object of the present invention to provide a process for applying adhesive close to both edges of a web of material which is not accompanied by a reduction in the strength of the bond formed between the web of material and the absorbent article to which it is attached.
It is still another object of the present invention to provide a process for applying adhesive close to the edge of a web of material that has a mechanism for controlling the amount of adhesive applied when there are variations in the raw materials used in the process which require different amounts of adhesive to be applied in order to form a secure bond with the web of material.
These and other objects of the present invention will be more readily apparent when considered in reference to the following description and when taken in conjunction with the accompanying drawings.